Method and apparatus for forming internal helical ribbing in a tube



Dec. 6, 1966 P. H. KOCH ET AL 3,289,451 METHOD AND APPARATUS FOR FORMING INTERNAL HELICAL RIBBING IN A TUBE Filed May 22, 1964 FIG.2

L L 28 34 W I J 15-. -7 36 25 L f -20 C E'ATTORNEY United Stae This invention relates to a method and an apparatus for forming internal helical ribbing in tubing, especially tubing of steam generating and superheating equipment utilizing a vaporizable fluid. Ribbed tubing of this type is disclosed in U.S. Patent No. 3,088,494, entitled Ribbed Vapor Generating Tubes of Paul H. Koch, Edward A. Pirsh and Howard S. Swenson, issued May 7, 1963, and assigned to The Babcock & Wilcox Company.

Internal helical ribs may be formed integrally in tubes by dnawing the tube through a die while a spiral-grooved mandrel is positioned in the die orifice. In this method, a freely rotatable, spiral-grooved mandrel will rotate on its longitudinal axis as the tube is drawn through the die orifice to the extent such mandrel rotation is not opposed by frictional forces. When the opposing frictional forces are quite large, as is often the case, shear forces may break the mandrel and/or damage the ribs as they are being formed. According to the present invention, this problem is solved by applying a constant torque to the mandrel to overcome the friction forces, thereby compensating for frictional resistance and promoting proper mandrel rotation. As a result, it is possible to form helical ribs, even ribs having a relatively short lead without subjecting the mandrel and the ribs to damaging stresses.

Tube drawing apparatus constructed according to the present invention includes means, drivingly connected to the mandrel, for rotating the mandrel, and applying torque thereto.

The various objects, features and advantages of the invention will appear more fully from the detailed description which follows, taken in connection with accompanying drawings, forming a part of the present application, and in which:

FIG. 1 is a longitudinal sectional view of an internally ribbed tube having a single continuous helical groove made according to the method and utilizing the apparatus of the present invention;

FIG. 2 is an elevational view of tube drawing apparatus constructed and arranged according to the invention;

FIG. 3 is a schematic illustration of a device included in the apparatus of FIG. 2 for applying torque to the mandrel according to the invention;

FIG. 4 is an enlarged fragmentary elevation, mostly in section, taken along line 4-4 of FIG. 2 through the tube and die of the apparatus, illustrating the tube sizing and rib-forming parts in detail. 7

In FIG. 1 there is illustrated a helically ribbed tube 10 of the type which can be formed by the method and apparatus of the present invention. Such tubes are specially constructed and proportioned to assure nucleate boiling or superheating of the fluid flowing therethrough. They can be advantageously used within the high input flow circuits of a steam generating and superheating unit.

The tube 10 is formed in suitable lengths of carbon or alloy steel tubing of circular cross section. The inner wall surface 12 of the tube is formed throughout its length with a single continuous helical groove 14, although it is recognized that the invention can also be practiced in the forming of multiple continuous helical grooves. The formation of the groove 14 provides a continuous series of helical lands or ribs 16, one between each turn or convolution of :the groove 14, all of which is explained more 7 J ii 3,289,451 Patented Dec. 6, 1&66

fully in the previously cited US. Patent No. 3,088,494.

In the tube-drawing apparatus of FIG. 2, numeral 20 designates a draw bench for cold-drawing metal pipe and tube blanks. Draw bench 20 is provided with a drawing die 22 (see FIG. 4) which is suitably secured by a clamping ring 23 in a supporting die head 24 located generally at the longitudinal midpoint of the bench. There is also a trough-like tube support 25 for holding tube blanks in horizontal alignment with the die orifice.

Mounted atop the draw bench 20 is a carriage 26 having jaws 27 for securely gripping the leading end of the tube blank. The carriage 26 is slidably mounted on tracks 28 which extend lengthwise of the draw bench 20, between the die head 24 and one end of the bench 20. At the latter location there is mounted a reversible motor 30 which is in driving engagement with carriage 26, as shown, through an upper pulley 32, a belt 34, a lower pulley 36, and a screw shaft 38. The carriage 26 has suitable threads (not shown) in cooperative engagement with the threads of the screw shaft 38 so that normal operation of the motor 36 in one direction of rotation drives the carriage away from the die head 24 as the tube 10 is drawn through the die 22. Reversing rotation of the motor 30 moves the carriage 26 in the opposite direction, i.e., toward the die head 24, which movement may be effected for example, after a tube has been drawn and it is desired to reposition the carriage 26 adjacent the die head 24 for the start of another drawing operation. It should be understood, however, that the invention is not limited to any particular pulling means for drawing the tube 10 through the die 22.

Referring now to FIG. 4, the die 22 has an orifice 22A suitably sized to effect a reduction of wall thickness and outside diameter of tube 10. The die 22 is operatively associated with a back-supported, rotatable mandrel 40 within the tube and positioned coaxially within the die orifree to define therewith a restricted annular passageway through which the tube 10 is drawn. The mandrel 40 is secured to the end of a rotatable mandrel bar 42, as by brazing; but other securing means may also be employed with satisfactory results. The mandrel 40 is of the so-called helical or spiral-grooved type, being provided with helical forming surfaces 44. The latter are adapted to cooperate with the die 22 to form internally of the tube 16, a helical groove 14 having intermediate helical ribs 16. The forming of the ribs 16 is accomplished by the drawing operation, at the same time the wall thickness and outside diameter of the tube are reduced.

Although the mandrel 40 is rotatable, it is secured against axial movement relative to the die 22. To this end, the mandrel (bar 42 is adjustably secured to an encompassing chuck 46 which, in turn, is mounted for rotation between a spaced pair of stationary annular housings 48. The stationary housing 48 are each provided interiorly thereof with a thrust bearing (not shown) which secures the chuck 46, and prevents axial movement of the mandrel bar 42 and the mandrel 40, while at the same time permitting them to rotate unitarily relative to the housings.

Shown in FIG. 3 is a chain drive and gear system whereby unidirectional rotational motion is transmitted to the chuck 46 by a pitch chain 52 having links 54 which engage cogs 56 of a driven sprocket wheel 58 and also the cogs 60 of a driving sprocket wheel 62. The driven sprocket wheel 58 is secured in direct driving relation to the chuck 46, and the driving sprocket wheel 62 in adapted to be driven through a gear box 64 by a variable speed electric motor 66. A U-shaped take-up loop 72 is provided in chain 52 by a horizontally spaced pair of idler spnocket wheels 68 supported in spaced relationship atop a frame 70, with another idler sprocket wheel 74 riding in the saddle portion of the U-shaped loop 72 in the chain 52 supporting a depending weight 76. During proper and normal operation of the chain gear system, slack will develop in the lower portion of the moving pitch chain 52 between the sprocket wheels 58 and 62 which the suspended weight 76 will take it thereby transmitting a uniform force through the moving chain 52 and thus applying torque through the rotating chuck 46 to the rotating mandrel bar 42. The requisite mass of the weight 7 6 can be varied as necessary to obtain the torque required to overcome the frictional forces which resist rotation of the mandrel 40. The speed of the motor 66 is preferably adjusted to keep the weight 76 fully suspended in order that it will be applied to the chain 52. By this arrangement a constant torque is applied to the mandrel bar 42.

Internal helical ribs are formed in tubing and pipe according to the following procedure:

(a) The chuck 46 of FIG. 1 is loosened and the mandrel bar 42 moved through the chuck to the extreme lefthand position.

(b) The motor 30 is operated in reverse direction to reposition the carriage 26 adjacent the die head 24.

(c) The leading, or right-hand, end portion of a tube blank is reduced in well-known manner so that it will fit into and project through the orifice of the die 22, as the tube is inserted and supported in horizontal position.

(d) The jaws 27 of the carriage 26 are tightened on the reduced end portion of the tube blank so as to hold it securely.

(e) The mandrel bar 42 with mandrel 40 securely attached, is inserted into the open or left end of the tube blank and then moved forward until the mandrel 40 is properly positioned in the die orifice, seated against the tube wall after which the chuck 46 is secured to the mandrel bar 42.

(f) The mot-or 30 is operated in normal or forward direction in order to advance the carriage 26 to the right while pulling the tube 10 through the die 22; and, simultaneously,

(g) The motor 66 is operated in correlation with the operation of the motor 30, to transmit a turning motion to the mandrel bar 42 sufficient to overcome the friction between the mandrel 40- and the tube 10 which resists mandrel rotation, the speed of the motor 66 being adjusted to keep the weight 76 freely suspended so that a constant torque is applied through the mandrel bar 42 to the mandrel 40.

The method and apparatus of the present invention were experimentally applied with success to drawing a tube blank 1.023 inches in outside diameter with a wall thickness of 0.230 inch, the mandrel having an outside diameter of .480 inch and provided with four wide grooves having a spiral lead of 1.5 inches. The tube was successfully drawn with the aid of 25 lb.-ft. of applied torque to produce a tube having outside and approximate inside diameter of .879 inch and .487 inch, respectively, with wide ribs having a height in the range of between .028 inch and .032 inch, and a pitch of .385 inch, with a lead of 1.54 inches. Such alloy steel tubing heretofore could not be successfully drawn.

From the foregoing it can be seen that an improved method and apparatus has been provided for forming internal ribbing in tubing so as to produce tubes of p d quality and also to minimize wear or damage to the mandrel.

Although the invention has been shown in but one fonm, it will be obvious to those skilled in the art that it is not so limited, but that it is susceptible of various changes and modifications without departing from the spirit thereof.

What is claimed is:

1. Tube drawing apparatus comprising a draw bench, a die supported on said bench, a spiral-grooved mandrel, a bar for supporting said mandrel in operative association with said die, a device movably supported on said bench for pulling tubing through a passageway defined by said die and said mandrel, a chuck rotatably supported on said bench and adapted to grip said bar for rotation therewith, a motor, a chain gear system including a chain for transmitting unidirectional rotational motion from said motor to said chuck and further including a pair of horizontally spaced idler wheels spanned by a portion of said chain, and a freely rotatable weight suspended from said portion of said chain for transmitting said weight through said chain to apply a torque through said chuck to said bar and said mandrel.

2. In the method of forming internal ribbing in a metal tube, the steps of cold drawing said tube through a passageway defined by a reducing die and a rotatable spiral-grooved mandrel, reducing the outside diameter and wall thickness of said tube and forming the internal ribbing by permanently deforming the inner surface of the tube against said mandrel, and applying a constant torque to said mandrel simultaneously with said drawing.

3. In the method of cold forming an internal helical rib in the inner wall surface of an elongated metal tube, including the steps of drawing said tube between a reducing die and a rotatable spiral-grooved mandrel, reducing the outside diameter and wall thickness of said tube and forming the internal helical trib by permanently defomning the inner surface of the tube against said mandrel, rotating said mandrel incident to said rib forming about said longitudinal axis of said tube whereby frictional torces oppose the rotation of said mandrel, and applying to said mandrel a constant torque which is opposite to said frictional forces and at least equal thereto simultaneously with said drawing.

4. The method of cold forming internal helical ribs in metal tubing and the like comprising the steps of providing a reducing die and a rotatable spiral-grooved mandrel, positioning one end of a tube in said die, inserting said mandrel in said tube and in operative association with said die, reducing the outside diameter and wall thickness of said tube while forming said ribs by pulling said tube through said die while rotating said mandrel about the longitudinal axis of said tube incident to forming ribs therein, with frictional forces opposing the rotation of said mandrel, and applying torque to said mandrel in opposition to said frictional forces, said torque being applied simultaneously with the pulling of said tube.

References Cited by the Examiner FOREIGN PATENTS 3/1944 Australia. 1/1963 Maughan. 

1. TUBE DRAWING APPARATUS COMPRISING A DRAW BENCH, A DIE SUPPORTED ON SAID BENCH, A SPIRAL-GROOVED MANDREL, A BAR FOR SUPPORTING SAID MANDREL IN OPERATIVE ASSOCIATION WITH SAID DIE, A DEVICE MOVABLY SUPPORTED ON SAID BENCH FOR PULLING TUBING THROUGH A PASSAGEWAY DEFINED BY SAID DIE AND SAID MANDREL, A CHUCK ROTATABLY SUPPORTED ON SAID BENCH AND ADAPTED TO GRIP SAID BAR FOR ROTATION THEREWITH, A MOTOR, A CHAIN GEAR SYSTEM INCLUDING A CHAIN FOR TRANSMITTING UNIDIRECTIONAL ROTATIONAL MOTION FROM SAID MOTOR TO SAID CHUCK AND FURTHER INCLUDING A PAIR OF HORIZONTALLY SPACED IDLER WHEELS SPANNED BY A PORTION OF SAID CHAIN, AND A FREELY ROTATABLE WEIGHT SUSPENDED FROM SAID PORTION OF SAID CHAIN FOR TRANSMITTING SAID WEIGHT THROUGH SAID CHAIN TO APPLY A TORQUE THROUGH SAID CHUCK TO SAID BAR AND SAID MANDREL. 